impossible in ghc 6.2

Greetings.  Ran into a bug with ghc 6.2 on some code that most probably
used to work.  I'm using a newer version of the fgl, from what I was
using before, though.  This only happens with -O2, and I don't think
-dcore-lint or -dppr-debug do anything interesting.  It happens with or
without the heap-size flag.  The usual problem with sharing Aetion code
applies here, so I can't send you the files.  I'm glad to help track
this down in other ways, though.

/usr/bin/ghc --make -O2 -dcore-lint -dppr-debug -fwarn-name-shadowing
-fglasgow-exts -fwarn-incomplete-patterns -package lang -package data 
-package fgl -H4564m -fallow-overlapping-instances -i/usr/lib/HUnit
-i/usr/lib/happy-1.13 -i/usr/lib/HUnit Main.hs




ghc-6.2: panic! (the `impossible' happened, GHC version 6.2):
        cgPanic
    ww {- v scVK -}
    static binds for:
    AbstractSyntax.zdwmakeConcreteRelInst {- v rcFr -}
    zdwshowsPrec5 {- v rcFt -}
    zdj {- v rcFv -}
    a {- v rcFx -}
    a1 {- v rcFz -}
    a2 {- v rcFB -}
    a3 {- v rcFD -}
    a4 {- v rcFF -}
    a5 {- v rcFH -}
    a6 {- v rcFJ -}
    a7 {- v rcFL -}
    a8 {- v rcFN -}
    a9 {- v rcFP -}
    a10 {- v rcFR -}
    a11 {- v rcFT -}
    a12 {- v rcFV -}
    a13 {- v rcFX -}
    a14 {- v rcFZ -}
    a15 {- v rcG1 -}
    a16 {- v rcG3 -}
    a17 {- v rcG5 -}
    a18 {- v rcG7 -}
    a19 {- v rcG9 -}
    a20 {- v rcGb -}
    a21 {- v rcGd -}
    a22 {- v rcGf -}
    a23 {- v rcGh -}
    a24 {- v rcGj -}
    a25 {- v rcGl -}
    AbstractSyntax.zdwshowsPrec {- v rcGn -}
    lvl {- v rcGp -}
    lvl1 {- v rcGr -}
    lvl2 {- v rcGt -}
    lvl3 {- v rcGv -}
    lvl4 {- v rcGx -}
    lvl5 {- v rcGz -}
    lvl6 {- v rcGB -}
    lvl7 {- v rcGD -}
    lvl8 {- v rcGF -}
    lvl9 {- v rcGH -}
    lvl10 {- v rcGJ -}
    lvl11 {- v rcGL -}
    lvl12 {- v rcGN -}
    lvl13 {- v rcGP -}
    lvl14 {- v rcGR -}
    lvl15 {- v rcGT -}
    lvl16 {- v rcGV -}
    lvl17 {- v rcGX -}
    lvl18 {- v rcGZ -}
    lvl19 {- v rcH1 -}
    lvl20 {- v rcH3 -}
    lvl21 {- v rcH5 -}
    lvl22 {- v rcH7 -}
    lvl23 {- v rcH9 -}
    lvl24 {- v rcHb -}
    lvl25 {- v rcHd -}
    lvl26 {- v rcHf -}
    lvl27 {- v rcHh -}
    lvl28 {- v rcHj -}
    lvl29 {- v rcHl -}
    lvl30 {- v rcHn -}
    lvl31 {- v rcHp -}
    lvl32 {- v rcHr -}
    lvl33 {- v rcHt -}
    lvl34 {- v rcHv -}
    lvl35 {- v rcHx -}
    lvl36 {- v rcHz -}
    lvl37 {- v rcHB -}
    lvl38 {- v rcHD -}
    lvl39 {- v rcHF -}
    lvl40 {- v rcHH -}
    lvl41 {- v rcHJ -}
    lvl42 {- v rcHL -}
    lvl43 {- v rcHN -}
    lvl44 {- v rcHP -}
    lvl45 {- v rcHR -}
    lvl46 {- v rcHT -}
    lvl47 {- v rcHV -}
    lvl48 {- v rcHX -}
    lvl49 {- v rcHZ -}
    lvl50 {- v rcI1 -}
    AbstractSyntax.lvl51 {- v rcI3 -}
    lvl52 {- v rcI5 -}
    lvl53 {- v rcI7 -}
    lvl54 {- v rcI9 -}
    lvl55 {- v rcIb -}
    lvl56 {- v rcId -}
    lvl57 {- v rcIf -}
    lvl58 {- v rcIh -}
    lvl59 {- v rcIj -}
    lvl60 {- v rcIl -}
    lvl61 {- v rcIn -}
    AbstractSyntax.zdwmakeAbstRoot {- v rcIp -}
    zdwallNamesInMSszq {- v rcIr -}
    AbstractSyntax.zdwallNamesInMSszqzq {- v rcIt -}
    local binds for:
    w1 {- v scVD -}
    nns {- v scVJ -}
    SRT label AbstractSyntax.zdwallNamesInMSszqzq {- v rcIt -}_srt
 
Please report it as a compiler bug to glasgow-haskell-bugs@xxxxxxxxxxx,
or http://sourceforge.net/projects/ghc/.
-- 
Isaac Jones <isaac.jones@xxxxxxxxxx>
Aetion